Reignition system for jet engine



Sept. 30, 1969 c. R. SCHAFER REIGNITION SYSTEM FOR JET ENGINE Filed Maw 29. 1967 INVIQN'IUR: CURTISS R. SCHAFER AT T'Y United States Patent U.S. Cl. 60--39.82 A 4 Claims ABSTRACT OF THE DISCLOSURE A system for detecting flameout in a jet engine and for automatically reigniting the engine immediately after the flameout has occurred.

The present invention relates to a system for detecting absence of flame in a jet engineand for reigniting the engine promptly upon detection of the loss of flame.

In the operation of jet engines a problem often arises from inadvertent extinguishing of the flame, a condition which is known as flameout. If the flameout is detected promptly, and before appreciable loss in rotor speed, it is possible to reignite the engine without difliculty. However, if the flameout is not detected promptly, the pilot must perform an elaborate ignition procedure to start the engine again. It would be desirable to. provide a system for immediately detecting a loss of flame and then promptly reigniting the engine before the rotor speed decreases to any great extent and the satisfaction of this desire, therefore, constitutes the principal object of the present invention.

In applicants copending U.S. application Serial No. 450,342 filed April 23, 1965, and assigned to the same assignee as the present invention an apparatus is disclosed for determining the number of ions collected by one or more charged electrodes disposed in theflowing hydrocarbon flame of a jet engine in order to measure the engine thrust. If the flame is extinguished so that the ion content is reduced or falls to zero, a detecting apparatus of this general type could be employed to provide a prompt and reliable indication of flamout. In accordance with the present invention, the absence or sharp decrease in ions is further used to trigger immediately an ignition circuit in order to reignite the jet engine.

Another object of the invention is, therefore, to provide apparatus for promptly detecting the absence or decrease of ion content of the exhaust gases produced by a turbojet engine and for reigniting the jet engine immediately upon the occurrence of such a condition.

The invention has for another object the provision of an apparatus for automatically reigniting a jet engine immediately upon the occurrence of flameout.

In accordance with the present invention, the foregoing and other objects are realized by providing a detecting apparatus responsive to the ion content of the exhaust gases produced by a turbojet engine. This apparatus comprises one or more electrode arrays located at the exhaust or outlet end of the engine for developing an electrical current proportional to the product of the mass and velocity of the ions in the latter gases. If the ion content of the exhaust gases falls below a preselected minimum value an electrical signal is automatically supplied to a reignition circuit for igniting the jet engine.

The invention, both as to its organization and manner of operation, together with further objects and advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawing wherein the single figure illustrates somewhat diagrammatically a longitudinal cross-sectional view taken through a typical jet engine and further illustrates ice schematically an ion detection and reignition system characterized by the features of the present invention.

- Referring now to the drawing a turbojet engine identified generally by the reference numeral 10 is there shown in somewhat diagrammatic form as comprising a housing or casing 11 containing a compressor 12 of conventional construction having its outlet 13 connected to deliver compressed gases to a combustion chamber 14 where the gases are heated and expanded for delivery to a turbine inlet 15. The outlet 16 of the turbine is connected to a tailpipe inlet 17 located upstream from a conventional afterburner 18. Gases from the tailpipe flow through a tailpipe outlet 19 located downstream from the iafter burner and through a throat 20 to a jet nozzle out- For the purpose of detecting ions in the exhaust gases n from the engine, an electrode array is indicated generally by the reference numeral 22 and includes one or more electrodes. If several electrodes are used they preferably take the form of uniformly spaced apart, identical, sampling electrode assemblies 23 provided either in the tailpipe inlet section 17 (as shown in the drawing) or in the outlet section 19. The electrode assemblies could also be employed to sample the flame in the combustion chamber 14 as is described in the copending application Serial No. 450,342 referred to above. Each of the electrode assemblies 23 is constructed as described in detail in the latter copending application wherein these assemblies have also been assigned the reference numeral 23. The electrode assemblies develop an electrical current proportional to the ion concentration in the gases of the jet engine 10. Each electrode assembly 23 is preferably mounted on the wall or casing 11 of the engine in the manner described in the copending application. Moreover, as is mentioned in the latter application, the num ber of electrodes in the array 22 is sufiicient to average out the effects of turbulence in the stream of exhaust gases. The probes of the electrode assemblies are electrically connected in parallel so that their combined output is proportional to the sum of the ionization currents produced by the electrodes. The parallel connected electrode assemblies 23 are electrically connected through conductor means 24 to a snap action regenerative or switching type amplifier 25 having its output connected to supply current to the operating coil 26a of a relay 26. As is described in the aforementioned application Serial No. 450,342 the electrodes may be selectively polarized to collect either negative or positive ions as desired.

The relay 26 includes a set of contacts 26b-26c for controlling application of power from a conventional AC source, such as a volt, 400 cycle source generally employed on aircraft, via conductors 27, 28 and 29 to an electrical ignition system or circuit 30. The latter source also supplies power to a conventional DC power supply 31 via a conductor 32 and a common conductor 33 which is also connected to the ignition system 30 and to the amplifier 25. For the purpose of reigniting the engine 10 in the event of flameout, the output of the ignition system is connected via a conductor 34 to one or more igniters or spark plugs 35.

As long as a flame is present in the engine 10, the ion concentration in the exhaust gases causes the electrode array 22 to develop an input current to the amplifier 25 of suflicient value to create an output current for energizing the relay 26. Thus, with the engine 10 running normally, the relay 26 is energized so that its contacts 26b- 260 are open to break the circuit from the power supply conductors 27 and 28 to the ignition system conductor 29. If the engine flame is inadvertently extinguished, the ion concentration in the gases acting upon the electrode assemblies 23 immediately decreases sharply or disappears altogether so that the current developed by the 3 amplifier 25 is no longer suflicient to maintain the relay 26 energized. The contacts 26b-26c thus revert to their normally closed position to complete the circuit from the power supply conductor 27 to the input of the ignition system 30 via the conductors 28 and 29. The ignition system functions in well known manner in response to this application of power to develop an output for energizing the igniter 35, thereby to reignite the jet engine 10. Since the reignition occurs almost instantaneously after the flame has been extinguished, the rotor of the engine does not lose appreciable speed before the engine is reignited.

More specifically, under normal conditions the rotor of a jet engine must be externally rotated to a speed of about 9000 r.p.m. before the engine can be started. The normal operating speed may be in the order of 12,000 r.p.m. If the engine loses flame the rotor speed drops below 9000 r.p.m. in slightly more than one second. Capacitor discharge type units are used to provide the spark for the igniter or igniters 35. Such units require approximately one second to charge the capacitor sufficiently to the relay, the ignition system is automatically started.

" Moreover,'th'e output signal from the amplifier can be produce an ignition spark. Thus, it is important that the fiameout be detected and the reignition process started almost instantaneously after the flameout has occurred if the rotor is to be prevented from losing so much speed that the engine cannot be reignited. If the rotor slows down excessively before the reignition begins, the pilot must shut off the fuel for several seconds to purge the engine of combustible gases in order to avoid a violent explosion within the engine. Thereafter, the external rotor drive must be employed to restore the rotor speed to about 9000 r.p.m. These disadvantages are avoided by the system of the present invention because it has been found that the response time required for the detector or electrode array 22 to react to the loss of flame is 5 milliseconds or less, the response time of the amplifier 25 is 15 milliseconds or less and the response time of the relay is 7 milliseconds or less so that the total response is about 27 milliseconds or less. This means that the reignition may be started promptly after the flameout occurs and before sufficient time has passed to cause the rotor to decrease its speed below 9000 r.p.m.

It should also be observed that the use of a relay having normally open contacts which are maintained closed by the output current of the amplifier 25 makes the system virtually foolproof. Thus, in the event of a power failure to the amplifier or in the event of any other malfunction in the amplifier that results in de-energization of used as an auxiliary control signal to indicate the presence of flame in the engine. For example, this signal can be used to control an autopilot.

While a particular embodiment of the invention has been illustrated and described, it will be recognized that many modifications and changes will readily occur to those skilled in this art and it is, therefore, contemplated by the appended claims to cover any such modifications and changes as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. For use ina jet engine having means for producing a flame to maintain said engine in normal operation, said engine being subject to flame out, an ignition system for igniting said engine as a result of flame out, ion detecting means for detecting the ion content of exhaust gases and consequently the absence of flame in said engine after flame out, and means controlled by said detecting means for energizing said ignition system in response to the detection of absence of flame, said detecting means and energizing means being constructed and arranged to operate within a total time of about 27 milliseconds.

2. The apparatus defined by claim 1 wherein the detecting means comprises at least one electrode assembly for detecting the concentration of ions in the exhaust gases from the engine and operable to produce an indication within 5 milliseconds after the loss of flame.

3. The apparatus defined by claim 2, said energizing means being constructed and arranged to produce an output signal within 22 milliseconds after said indication.

4. The apparatus defined by claim 3 wherein said signal is used as an auxiliary control signal.

References Cited UNITED STATES PATENTS 2,496,502 2/1950 Steensma. 2,689,455 9/1954 Stockinger. 2,743,577 5/1956 Malick 340228.1 XR 2,820,945 1/1958 Marsden.

JULIUS E. WEST, Primary Examiner U.S. Cl. X.R. 

